This invention relates to a drop-out compensation system for the replay of television signals recorded on magnetic tape. The term "drop-out" is a known term in the television signal production art referring to the loss of signal occurring as a result of discontinuities in a signal caused by inconsistencies in the recording medium. Such inconsistencies may occur as a result of dirt on the magnetic tape or possibly as a result of a gap in the oxide layer of the tape.
The effect of drop-outs on a displayed television picture is to cause flashes in the displayed picture. To minimise the visibility of flashes on the displayed picture, various techniques have been used to compensate for the effects of drop-outs.
Detection of a "drop-out" can be arranged by monitoring the RF carrier signal used as the recording carrier in the video tape recorder (VTR).
A common form of compensation when a "drop-out" is detected is to effect repetition of the picture signal line preceding the drop out by the use of some storage medium.
To insert information from the previous television line or lines the drop out compensator (DOC) includes a delay circuit or store of one picture scanning line duration continuously fed with the replayed video signal; when a drop out occurs the signal at the output of the one line delay circuit is substituted, so that the missing picture information in a scanning line is replaced by that from a scanning line above that in which the drop out occurred, or more often from information occurring at least two lines above.
Such a system is described in British Pat. No. 1,436,757 (U.S. Pat. No. 3,949,416). Even with such compensation, when stationary images are being produced the compensated drop outs may still be noticeable.